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Derm Rheum > Micro of Staph - Cross > Flashcards

Micro of Staph - Cross Flashcards

1
Q

What do all Staph have that helps you identify them vs. strep?

A

Catalase (can degrade H2O2)

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2
Q

What type of infection(s) does Staph epidermidis normally cause?

A

Prosthetic hardware/IV catheter infections, endocarditis

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3
Q

What type of infection(s) does Staph saprophyticus cause?

A

UTI; 2nd most common cause

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4
Q

People with arthritis or other joint damaging diseases are at increased risk for osteomyelitis. Why?

A

Joint damage exposes underlying fibronectin/laminin, Staph aureus can easily adhere to the glycoproteins

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5
Q

What area of the skeleton is especially vulnerable for osteomyelitis due to arthritis?

A

The vertebral column (lumbar especially)

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6
Q

What is the carrier state?

A

Individual harbors a potential pathogen and can be a source of infection for others

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7
Q

What is colonization?

A

Acquisition of a new organism and it may cause infection

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8
Q

What is colonization resistance?

A

Nonpathogenic resistant bacteria occupy attachment sites interfering with pathogenic bacterial colonization

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9
Q

Gram stain of S. aureus?

A

Gram positive cocci in clusters (grapelike)

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10
Q

Morphology of S. aureus?

A

Beta hemolytic; catalase(+), coagulase(+), ferments mannitol

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11
Q

What gene contains the sequence for the altered PBPs that confers methicillin resistance?

A

MecA

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12
Q

What serum do they use in the lab for the coagulase test?

A

Rabbit serum (she said to know this)

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13
Q

Where is the main site of colonization (on the body) for S. aureus?

A

The nose

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14
Q

Name all the S. aureus virulence factors (there are 10)

A

1) Staphyloxanthin
2) Coagulase
3) Hemolysins
4) Portein A
5) Teichoic Acid
6) Polysaccharide capsule
7) Peptidoglycan
8) Alpha toxin/Hemolysin
9) Panton Valentine (P-V) leukocidin
10) Gamma toxin/leukotoxin

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15
Q

What does staphyloxanthin do? What does it specifically do to the bacteria when on agar?

A

It inactivates superoxides produced by WBCs; it confers the gold color unique to S. aureus

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16
Q

What does coagulase do?

A

converts prothrombin–>thrombin; this delays neutrophil migration

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17
Q

What do hemolysins do?

A

Hemolyse RBCs and use their Fe2+ to grow

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18
Q

What does Protein A do?

A

Binds to the Fc portion of IgG to prevent complement activation; no C3b is produced so phagocytosis is greatly impaired

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19
Q

What do teichoic acids do?

A

Mediate the adherence of staph to mucosal cells

20
Q

What does peptidoglycan do?

A

Stimulates macrophages to produce cytokine storm/activate complement; causes the “septic shock” picture seen in S. aureus bacteremia

21
Q

What does P-V leukocidin do?

A

Pore forming cytotoxin that kills leukocyte by cell membrane disruption and causes tissue necrosis

22
Q

What diseases specifically does P-V leukocidin allow S. aureus to cause?

A

Necrotizing PNA and severe soft tissue/skin infection

23
Q

What does gamma-toxin/leukotoxin do?

A

Lyses phagocytes/RBCs

24
Q

What bacteria almost always causes an abscess?

A

S. aureus

25
Q

What virulence factors cause scalded skin syndrome?

A

Exfoliative toxins A and B

26
Q

What age group is scalded skin syndrome commonly seen in?

A

Newborns, 3-7 days of age

27
Q

What do exfoliative toxins A and B do to the body?

A

Protease that cleaves desmoglein; separates the epidermis at the granular layer

28
Q

What toxin causes S. aureus induced food poisoning? Describe the illness

A

Enterotoxin A; vomiting and watery, NON-BLOODY diarrhea

29
Q

Why is enterotoxin A so virulent?

A

It is heat resistant (brief cooking won’t destory it) and it is resistant to stomach acids

30
Q

Describe bullous impetigo

A

Seen in young children; flaccid bullae with clear yellow fluid that later becomes more turbid; rupture will leave behind a thin brown crust, commonly on the TRUNK

31
Q

What is the pathogenesis of Staph toxic shock syndrome?

A

Toxin mediated/superantigen, elicits large amount of IL-1, IL-2, and TNF-a release

32
Q

Common scenarios causing staph toxic shock syndrome?

A

Tampon use, nasal packing to stop epistaxis, post-op infection

33
Q

Blood cultures in Staph aureus toxic shock syndrome?

A

NEGATIVE 95% of the time

34
Q

Lethal complication of toxic shock syndrome, commonly seen in bacteremia (I know this question sucks)?

A

DIC

35
Q

Resistance seen in MRSA (mechanism of resistance)?

A

Change in PBPs in the cell membrane

36
Q

Resistance seen in VRSA (mechanism of resistance)?

A

D-ala replaced with D-lactate; vancomycin can no longer affect it

37
Q

Resistance seen in VISA (mechanism of resistance)?

A

Synthesis of unusually thickened cell well

38
Q

What is the D-test?

A

Culture bacteria on a plate with a disk of clindamycin and one of erythromycin. If area around the clinda is “D-shaped” the test is +, indicates inducible resistance (DON’T USE CLINDA)

39
Q

Generalized tx guidelines for Toxic shock syndrome?

A

Aggressive fluid replacement therapy, vasopressors (can cause distal necrosis). Abx and surgical debridement, if necessary

40
Q

Why do you use clindamycin in the treatment of TSS? What other abx shares the same function?

A

It suppresses toxin synthesis; can also use Linezolid

41
Q

Morphology of Staph epidermidis?

A

Catalase(+), Coagulase(-), non-hemolytic, urease(+), does NOT ferment mannitol, Novobiocin sensitive

42
Q

What is the main pathogenic mechanism of staph epidermidis?

A

It has adhesins for interaction with surface proteins; once it attaches to a catheter or prosthetic device it secretes a polysaccharide biofilm (insulates it from phagocytosis/abx)

43
Q

You get a blood culture positive for Staph epidermidis. The patient is afebrile and in no distress. What do you think?

A

Contamination; Staph epi is all over the skin and commonly contaminates blood cultures

44
Q

Staph saprophyticus morphology?

A

Catalase(+), Coagulase(-), non-hemolytic, urease(+), does NOT ferment mannitol, Novobiocin resistant

45
Q

Novobiocin test. Distinguishing between which bacteria?

A

Staph epidermidis (SENSITIVE) vs. Staph saprophyticus (RESISTANT)

46
Q

What 2 morphologic characteristics distinguish S. aureus form all other staphylococci?

A

Coagulase (+) and B-hemolysis

47
Q

Pathogenesis of enterotoxin-A mediated food poisoning

A

Superantigen in the GI tract, causes massive IL-1 and IL-2 release from macrophages/helper T cells

Derm Rheum (39 decks)

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